CHAPTER Protocols and IEEE Standards
Chapter Objectives • Discuss different media level protocols including their functioning • The major protocols chosen for discussion are as follows: – CSMA/CD, token passing and polling • Discuss the IEEE standards that apply to LANs based on different protocols
Chapter Modules • LAN Protocol: Carrier Sense Multiple Access/Collision Detection (CSMA/CD) • LAN Protocol: Token Passing • LAN Protocol: Polling • IEEE Standards
END OF CHAPTER INTRODUCTION
MODULE IEEE and Lower Layer LAN Protocols
IEEE Background • Institution of Electrical and Electronic Engineering (IEEE) • A professional non-profit organization • Project group 802 under IEEE – Entrusted with the task of setting standards relating to physical and logical links of nodes in a network • Standard mostly applies to the Physical and Data Link layers • Example – IEEE 802. 3 standard for the Ethernet bus network
The ISO-OSI Model Recalled • Models the end-to-end communication process • It is a seven-layer model • Proposed by International Standard Organization (ISO) • The model is known as Open Systems Interconnect (OSI) • IEEE sets the standards at the lower levels of the ISO-OSI model
ISO-OSI Seven Layer Model Layer 7 Application Layer 6 Presentation Layer 5 Session Layer 4 Transport Layer 3 Network Layer 2 Data Link Layer 1 Physical Focus of IEEE 802 Source: http: //starter. sdsu. edu/remote/demo/osi-tcp. html
Comparison of ISO-OSI Model and the DOD (TCP/IP) Model Source: http: //starter. sdsu. edu/remote/demo/osi-tcp. html Application Presentation Application Session Transport Host-to-Host Network Internet Data Link Physical Network Access
Layer Reference to Protocol Application Presentation Application FTP, Telnet, SMTP, HTTP, SNMP. . Session Transport Host-to-Host TCP, UDP Network Internet IP, ICMP Data Link Network Access Ethernet, Token-Ring. . . Physical Source: http: //starter. sdsu. edu/remote/demo/osi-tcp. html
Network Protocols Source: www. networkmagzine. com
Another Look at Network Protocols Source: www. networkmagzine. com
Network Protocols in the TCP/IP Model Source: www. networkmagzine. com
IEEE 802 Focus • OSI Reference – Data Link layer – Physical layer • Areas of applications – Network cards and cables – WAN connectivity etc. • Different subgroups under 802 that focus on different activities of the LAN
IEEE 802 Subgroups and their Responsibilities • 802. 1 – Internetworking • 802. 2 – Logical Link Control (LLC) • 802. 3 – CSMA/CD • 802. 4 – Token Bus LAN Continued
IEEE 802 Subgroups and their Responsibilities (Cont. ) • 802. 5 – Token Ring LAN • 802. 6 – Metropolitan Area Network • 802. 7 – Broadband Technical Advisory Group • 802. 8 – Fiber-Optic Technical Advisory Group Continued
IEEE 802 Subgroups and their Responsibilities (Cont. ) • 802. 9 – Integrated Voice/Data Networks • 802. 10 – Network Security • 802. 11 – Wireless Networks • 802. 12 – Demand Priority Access LANs – Ex: 100 Base. VG-Any. LAN
Ethernet Protocol Standards • 10 Mbps – IEEE 802. 3 • 100 Mbps – IEEE 802. 3 u • 1 Gbps – IEEE 802. 3 ab – Uses all 4 pairs of the RJ-45 cable (www. techfest. com/networking/lan/ethernet 1. ht m ) • 10 Gbps – IEEE 820. 3 ae
Wireless LAN Protocols • 802. 11 – 1 -2 Mbps, 2. 4 GHz, FHSS and DSSS • IEEE 802. 11 a – 54 Mbps, 5 GHz, Orthogonal Frequency Division Multiplexing • IEEE 802. 11 b – 11 Mbps, 2. 4 GHz, DSSS • IEEE 802. 11 g – 20+ Mbps, 2. 4 GHZ – 108 Mbps, 2. 4 GHz (Extreme G)
Newer Wireless Protocol • IEEE 802. 11 n
A Perspective of IEEE 802 Standards in Network Communication Logical Link Control (LLC) Media Access Control (MAC) 802. 2 802. 1 applies to both. 802. 3 802. 4 802. 5 802. 12
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MODULE LAN Lower Layer Protocol: IEEE 802. 3 Carrier Sense Multiple Access/ Collision Detection (CSMA/CD)
An Overview of CSMA/CD • CSMA/CD has two components as mentioned • First is the Carrier Sense Multiple Access (CSMA) component • Second is the Collision Detection (CD) component
CSMA Component of CSMA/CD • CSMA (Carrier Sense Multiple Access) – Check the bus for traffic – If the bus is free, then transmit – If it is busy, wait for a random period of time before attempting to transmit again
CD Component of CSMA/CD • Two stations may check the data bus simultaneously • Both may find the line free and engage in the transmission of data • Both transmission will collide • CD component will detect this collision – Inform the workstations of the collision • Each station will wait for a random period of time before attempting to transmit again
CSMA/CD Usage • Used extensively in bus LANs
CSMA/CD Standards • Highly standardized protocol • Different protocol standards for different speeds of communication • 10 Mbps Ethernet standard – IEEE 802. 3
IEEE 802. 3 • 10 G bps Ethernet – IEEE 802. 3 z • 1 G bps Ethernet – IEEE 802. 3 ab • 100 M bps Ethernet – IEEE 802. 3 u • 10 M bps Ethernet – IEEE 802. 3
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MODULE LAN Lower Layer Protocol: IEEE 802. 4 Token Bus Protocol
Token Bus Token Client Server Client A token is distributed to each client in turn. Client
Token Bus Data Pickup • A token is sent from one node to the other • The client wanting to transmit grabs an empty token • Data is attached • Token leaves for the next node and its travel on the bus until it reaches the Cont. address to which the data is destined
Token Bus Data Delivery • • • Token delivers the data to the addressee Acknowledgement is returned to the sender Token is passed to the next node The process continues If there is an error in delivering the information, a request for retransmission attached to the token and it is sent to the sender
Token Bus Standard and Applications • IEEE 802. 4 • It can be used in both broadband baseband transmission
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MODULE LAN Lower Layer Protocol: IEEE 802. 5 Token Passing Protocol
Token Passing Protocol in Operation Circulating Token A D B Workstation Server C Workstation • No collisions
Comparison with CSMA/CD • Absence of collision • Offers a systematic method of transmitting information • In theory, it is superior to CSMA/CD • More sophisticated to implement • Protocols used in the newer and most popular networks are, however, based on CSMA/CD
The Token • Token – Data packet that could carry data – Circulates around the ring – Offers an opportunity for each workstation and server to transmit data
The Transmitting Workstation • Waits for a free token in order to be able to attach the data to be transmitted to the token • On finding a free token, attach the following: – – – Sender’s address Receiver’s address Data block to be transmitted Error checking details etc.
At the Receiving End • Data is received and checked for errors • Outcomes at the receiving end – Data received without errors – Date received with errors
Error-free Delivery of Data • An acknowledgment is attached to the token • Acknowledgment is passed to the sender • Token is set free for other nodes to transmit information • At this time, the next workstation on the ring will receive an opportunity
Correcting Errors in Delivery • A request for retransmission is attached to the token • Token carries the message for retransmission to the sender • The data is thus retransmitted
Token Regeneration • The token is regenerated at regular intervals to sustain the timing of circulation of the token
Usage of Token Passing • Used extensively in ring LANs – Especially in the IBM token-ring LAN • A version of this protocol is also used on certain types of bus LANs – Token-bus networks • Used in large fiber-optics backbones – Used for the construction of very large networks
Usage in Practice • Used in backbones • Uses in a number of IBM shops • Overall, the usage of Ethernet surpasses the usage of Token-Ring networks that are based on the Token-Passing protocol
Token Passing Standards • IEEE 802. 5 – For the token-ring LANs • IEEE 802. 4 – For the token-bus LANs • A FDDI protocol is used on large fiberoptic ring backbones
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MODULE WAN Protocol: Token Passing on FDDI
ANSI X 3 T 9. 5 Protocol • This wide are network protocol is standardized by ANSI • Works similar to Token Passing Protocol • Used in FDDI and CDDI backbone networks • Usually implemented in dual-ring format for fault tolerance
Reliability: Counter Rotating Ring Br ak e By-pass the defective segment of the cable
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MODULE LAN Lower Layer Protocol: Polling
Polling in Operation Server WS A WS B Data Delivery WS : Work Station Poll WSC Acknowledgement or Request for retransmission
Polling and Delivery of Data • Server polls each workstation • A workstation responds by sending a data packet • Data packet is delivered to the address found in the packet
At the Receiving End • If there are no errors : – Acknowledgment is returned to the sender – The server then continues with the polling process • If there are errors: – A request for retransmission is conveyed to the sender – The entire transmission process is then repeated
The Usage of the Polling Protocol • Mainly used in multi-user microcomputer – Based on the physical and logical star topologies • Example – A multi-user microcomputer running the Unix operating systems
Difficulties in Implementing Polling in LANs • It is difficult to implement the polling protocols in large networks with multiple segments • Multiple servers in different segments may have problems in polling all the workstations
Polling Implementations • True multi-user systems such as a Unix based multi-user system
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END OF MODULE END OF CHAPTER
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